This invention relates to a control for a motor vehicle window wiper system and particularly to such a control for a system having a pair of potentially interfering wiper blades driven by separate electric motors. In such a system, unlike the more traditional single motor system with mechanical interlocking drive means, there is need for apparatus to ensure that the wiper blades stay in synchronized wiping patterns and do not interfere with each other, even if one of the blades is stopped or otherwise strays far out of synchronization.
Prior art systems have been described which synchronize a pair of separately driven wiper blades on a vehicle window by sensing the arrival of each wiper blade at a predetermined point in its wiping pattern and preventing the first wiper blade to reach that point from proceding until the other wiper blade has also reached its corresponding point. Such points have been suggested as one or both ends of the wipe cycle at the points of reversal of blade motion. It has also been suggested that more points might be used throughout the cycle.
The suggestions of the prior art have been good, but they can be improved. For example, synchronization only at end points might cause noticeable pauses in the wipe cycle of one wiper blade if the other is driven at an appreciably slower rate or through a significantly longer path. Addition of more numerous check points might also cause annoyingly uneven wiper blade movement. Finally, stoppage of one blade will not necessarily stop the other blade, with the resulting possibility of blade interference.